One conventional electromagnetic contactor is illustrated in FIG. 1. Designated at 1 is an attachment base molded of plastics, 2 a fixed laminated iron core composed of silicon steel plates, 3 a movable laminated iron core composed of silicon steel plates, 4 a control coil for imposing a driving force to attract the movable iron core 3 and the fixed iron core 2 against the force of a tripping spring (not shown), 5 a cross bar molded of plastics and having a rectangular window, the cross bar 5 supporting the mvoable iron core 3 on a lower end thereof, 6 a movable contact member inserted through the rectangular window of the cross bar 5, 6A a movable contact on one end of the movable contact member 6, 7 a presser spring for pressing the movable contact member 6, 8 a fixed contact member disposed in confronting relation to the movable contact member 6 and supporting on one end a fixed contact 8A, the movable contact 6A being movable into and out of contact with the fixed contact 8A, and 8B a terminal on the other end of the fixed contact member 8. When the contacts 6A, 8A are in contact with each other, a current flows from the fixed contact member 8 to the movable contact member 6. Denoted at 9 is a terminal screw for connecting the body of the electromagnetic contactor to an external circuit, 10 a base to which the fixed contact 8 is attached, 11 an arc cover disposed in covering relation to the electromagnetic contactor, 12 an arc generated between the fixed contact 8A and the movable contact 6A, and 13 a plurality of parallel metal extinguishing plates of a magnetic material which lie parallel to the surface of the fixed contact member 8 to which the fixed contact 8A is joined. The arrangement of FIG. 1 is symmetrical, and only a righthand portion thereof is shown in cross section.
When the control coil 4 is de-energized in the electromagnetic contactor thus constructed, the movable iron core 3 is separated from the fixed iron core 2 by a tripping mechanism (not shown), and the cross bar 5 is positioned as shown in FIG. 1. The fixed contact 8A and the movable contact 6A are separated from each other while an electric current is flowing therethrough to produce the arc 12 between the contacts 8A, 6A as shown in FIGS. 1 and 3. The arc 12 is attracted to the magnetic metal extinguishing plates 13, and moved successively through positions 12A, 12B as shown in FIG. 2. The arc 12 is finally extinguished between the metal extinguishing plates 13 to thereby cut off the current.
The conventional power switch (electromagnetic contactor) operates in the foregoing manner. When the arc is extinguished, only those of the parallel metal extinguishing plates 13 which are positioned between the movable contact member 6 and the fixed contact member 8 are involved, but not all of the metal extinguishing plates 13 are utilized. Therefore, the circuit breaking performance is poor, and the contacts tend to wear at a high rate.